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The present invention relates to petroleum-well downhole completion, and more specifically to a system and method providing a deep-set electrically controlled subsurface safety valve assembly.
Once an oil or gas well has been drilled to total depth, and occasionally while drilling is still in progress, production of any hydrocarbons present in commercially available quantities can begin. Production is normally accomplished through a conduit, frequently referred to as production tubing, which is significantly smaller in diameter than the hole that has been bored into the earth. This allows for production at a satisfactory rate while also permitting installation of various types of ancillary equipment inside the wellbore. For example, the wellbore itself may be six to sixteen inches in diameter at the surface (where the well penetrates the earth), typically becoming incrementally smaller at various depths, while the production tubing may have a diameter of no more than one to ten inches. The wellbore is typically lined with a metal casing cemented in place to preserve the integrity of the drilled hole. The casing may extend from the surface to the top of the production zone (i.e., hydrocarbon-bearing geologic formation), but more usually reaches all the way to the bottom of the well. In this latter instance, the casing must be perforated to allow the oil or gas to flow into the wellbore.
At the surface, a casing head flange is typically fixed to the top of the casing. To this casing head is then affixed a wellhead assembly, sometimes called a xe2x80x98Christmas treexe2x80x99, through which access to the well is controlled. The production tubing runs from the production zone to a control valve on the wellhead, which in turn connects to outlet piping that will carry the oil or gas to an on-site storage facility to await removal. In the case of an offshore well, the submerged wellhead may be little more than a than a flange or other device that seals off the casing just above the mudline (top layer of the ocean floor) or in a submerged completion may constitute the entirety of the well head including the xe2x80x98Christmas treexe2x80x99 and other wellhead production and completion equipment and controllers. In non-submerged completion it is typical for a conduit such as a flexible riser to be used to extend from the submerged wellhead portion at the ocean floor to the ocean surface to carry well production fluids to wellhead portions on a platform or barge positioned on the ocean surface. Well surface is used in onshore wells to designate that part of the well at or above the earths surface. In on shore wells the surface refers to that portion located at or above the submerged earth surface. The water or sea surface refers to the water level.
Damage to the wellhead can cause a drastic interruption of normal well production operations. In addition, damage may result in the leakage of hydrocarbons that pollute the surrounding environment and give rise to the danger of fire or explosion. Leakage is particularly undesirable at wells located offshore or in urban areas, where the unintentional escape of oil and gas can have potentially disastrous consequences for the local environment and its inhabitants. To prevent such damage, production wells are fitted with some downhole means of terminating the flow of petroleum products in the event of a loss of wellhead integrity. For example, the well may have a safety valve system for slowing down or shutting off the flow of petroleum products through the production tubing. In the event that the wellhead control valve is damaged, for example, an abnormally rapid flow rate through the safety valve will be detected, signaling a potential leakage problem and triggering safety-valve closure. Safety valves located below the wellhead are called subsurface safety valves.
A tubing retrievable safety valve (TRSV) is a tubing retrievable safety valve used for controlling production-tubing flow in the event of an emergency, or as required by a particular maintenance event. A TRSV is set and retrieved with the well tubing and is connected to control flow through the well tubing. TRSV""s are often positioned at subsurface depths of one to two thousand feet even in wells where the production zone is much lower. This sets the point of flow control well below the earth surface. When removable and reinstallation is required to service the TRSV the tubing length and type is a major factor in maintenance costs.
The TRSV may be hydraulically or electrically operated. In either case, TRSV""s are normally spring- or flow-biased so that a loss of valve control results in a closed, rather than open TRSV. In the case of a hydraulically operated TRSV, hydraulic fluid lines are run from the surface wellhead to provide the hydraulic pressure to keep the valve open. Maintaining a constant hydrostatic pressure over such a long run under adverse conditions can be problematic. Even under ideal conditions, the biasing device on the valve must be able to counter the head created by well over a thousand feet of hydraulic fluid filling the control-fluid lines from the surface. In offshore wells, the water depth adds to the length of control lines and in deep water wells can be significant. This may require the use of a more heavy-duty valve than is otherwise required.
Conventional electrically operated TRSV""s are powered by either downhole batteries or through xe2x80x98umbilicalxe2x80x99 electric lines from a source on the surface. Batteries, however, run down over time and must be replaced, adding to the well-maintenance costs. Although an umbilical does not have this disadvantage, it is subject to damage caused by other well equipment as it is moved in and out of the well.
Tubing length and type are even more important factors in the well costs associated with servicing subsurface safety valves in offshore wells.
Needed is a downhole safety valve assembly and method of use that is efficient, reliable, and economic to service and reduces the frequency of required maintenance. The present invention is directed to just such an assembly and method.
The present invention is directed to a assembly and method of providing an electrically operated downhole safety valve for use in production petroleum wells and similar operations. In one aspect, the system includes electrically operable in-line safety valve and tubing latch connected to a conduit or tubing of non-conductive material that incorporates a plurality of integral electrical conductors.
In another aspect, the invention is system and method of operating a downhole safety valve including the steps of providing a non-conductive conduit that houses electrical conductors, connecting the conductors to an electrically operated safety valve, connecting the conductors to surface mounted controller and power supply means, and operating the safety valve by variably providing power to the valve from the power supply. The method may also include the steps of monitoring the valve status, and providing an alarm for indicating a loss of power to the valve.
In another aspect, the invention also contemplates the use of an electrically operable tubing latch mounted on a tubing with embedded conductors, connecting the conductors to a power supply and operating the latch (locking and releasing) by variably supplying power to the latch. The invention also contemplates the steps of monitoring the status of the latch and incorporating the latch and safety valve in a single assembly.
In a further aspect the tubing with embedded conductors used in the safety valve and latch assemblies is of the type that is substantially continuous and can be lowered and raised from the well using a spooling device located at the surface without requiring that the tubing be separated into short sections.